Indicating device



Patented July 18, 1939 UNITED STATES PATENT OFFICE INDICATING DEVICE LoyE. Barton, Collingswood, N. J., assigner to Radio Corporation ofAmerica, a corporation of Delaware Application December 7, 1932, SerialNo. 646,074

9 Claims.

My invention relates to indicating devices and, more particularly, totuning indicators, dials, etc., adapted for use in radio receivers.

There recently has developed a very decided trend toward the use ofautomatic gain-control devices in radio receivers for the purpose ofmaintaining the sound output therefrom substantially constant inamplitude despite fading of the signal-carrier wave. Receivers soequipped, how- 10, ever, are'somewhat diicult to tune accurately to adesired carrier-Wave and recourse, heretofore,

has been had to the use of tuning-meters and the like to indicateresonance.

Tuning meters are relatively expensive. Also, they are of necessityfragile and do not stand up Well in service or during shipment of areceiver from the factory to its ultimate destination.

It is, accordingly, an object of my invention to provide an inexpensivetuning indicator particularly adapted for use in receivers of theautomatic gain-control type.

Another object of my invention is to provide a combined tuningindication and dial-lighting system.

Another object of my invention is to provide a system of the typereferred to that shall also be capable of giving an indication of theadjustment of a background noise control device.

In practicing my invention, as applied to a radio 30, receiver, I preferto provide the power-transformer, which supplies energizing potentialsto the various thermionic devices, the loudspeaker, etc., with an extrasecondary that is connected to one or more pilot lamps, which lamps mayor may not be utilized to illuminate the tuning dial, through theprimary winding of a small step-up transformer. The secondary of thetransformer is connected to the plate and cathode of a control tube, theimpedance of which is proportional to the potential applied to the gridthereof. The grid potential is obtained from a point in the receivercircuit, the potential of which varies according to the amplitude, orinversely as the amplitude in some instances, of an incoming signal.Accordingly, the impedance of the control tube and its elfectiveness asa load on the step-up transformer is a function of the signal amplitude,and the pilot lamp uctuates in brilliancy as the impedance changes.

I also so connect another pilot lamp of somewhat higher voltage acrossthe primary of the step-up transformer that its intensity decreases asthe intensity of the series lamp increases, and vice versa. A lamp ofthe same voltage as the seriesconnected lamp may, of course, be usedbut, in

(Cl. Z-20) such event, it is connected to an intermediate tap on theprimary of the transformer. The seesaw variation in intensity of the tWolamps permits quite accurate tuning of the receiver to the l peakresonance point.

Furthermore, according to my invention, the several lamps may bedifferently colored, they may both be utilized for dial-illumination, orthey may be disposed in any suitable position on the radio-receivercabinet Where they are visible to the operator. Translucent colorfilters may be utilized instead of colored lights, as well as variouscombinations of screens, mirrors, or lenses, without departing from thespirit of the invention.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, Willbest be understood from the following description of a spe-v cieembodiment, when read in connection with the accompanying drawing, inwhich Figure 1 is a diagrammatic view of a radio receiver including apreferred embodiment of my invention,

Fig. 2 is a fragmentary diagrammatic View of an alternative embodimentof my invention,

Fig. 3 is a front elevational view of a tuning dial showing theappearance thereof when the receiver is in the tuned in condition, and

Fig. 4 is a fragmentary sectional View of the receiver dial, taken alonga line corresponding to the line 4-4 in Fig. 3.

As hereinbefore pointed out, the primary object of my invention is toprovide a tuning indicator Which will enable a receiving system of theautomatic gain control type to be accurately brought into syntony with adesired incoming signal without reliance necessarily being placed uponthe volume of sound output therefrom.

As is Well known to those skilled in the art, the majority of radioreceivers of the automatic gain control type utilize a direct current,proportional to the amplitude of an incoming carrier wave, for thepurpose of controlling the bias applied to the input circuits of one ormore amplifying tubes. Although my invention may be applied to a radioreceiver equipped with a volume control system of substantially anywellknown type, I find it quite expedient to combine it with an improvedautomatic volume control system Which I also have invented.

Referring to Fig. 1 of the drawing, my improved volume control system isexemplified as applied to a second detector tube I of a radio receiverof the superheterodyne type. Specifically, the second detector includesa thermionic cathode 3, two diode electrodes 5 and 1, a control grid 9,and an output anode II. One of the diode electrodes, 5, is connectedback to the cathode through the secondary winding of an intermediatefrequency transformer I3 and a resistor I5. From a point on the resistorfurthest away from the cathode, a connection extends to the controlgrid, the connection, preferably, including a resistor I9 which impedesthe flow of grid intermediate frequency current.

The cathode is connected to the negative terminal 2| of a source (notshown) of uni-directional potential through a resistor 22, and theoutput anode II is connected to the positive terminal 23 of the samesource through the primary winding of an audio frequency outputtransformer 25, or through an equivalent transfer network.

In the specific receiver under discussion, a bleeder resistor 21 and theeld winding 29 of a loudspeaker are connected in shunt to the terminalsof the high potential source, and a point 3| between the resistor andthe winding is provided with a connection 33 to ground.

The resistor 22 in the cathode circuit is of such magnitude that thevoltage drop thereacross occasioned by plate current in the detectortube I during the no signal condition is greater than the drop acrossthe loudspeaker field winding 29. The reason for this difference inpotentials will be hereinafter apparent.

During the reception of signals, the intermediate frequency is impressedupon the diode plate 5 through the intermediate frequency transformerI3, it is rectified and direct current, varying at audio frequency, dueto modulation, flows in the resistor I5 included in the input circuit.The current is in such direction that the control grid 9 is negativelybiased with respect to the cathode of the tube and, as a result, thecurrent in the resistor 22 connected to the cathode decreases as asignal is tuned in, and the potential drop thereacross also decreases.

The second diode plate 1, as will be noted from an inspection of thedrawing, is connected over a resistor 35 to ground and the said plateis, therefore, at a negative potential, normally, with respect to thecathode 3. However, as the potential drop across the resistor connectedto the cathode decreases, the diode plate and the cathode approach thesame potential and, eventually, if the signal-carrier is of sufficientamplitude, the cathode will become negative with respect to the diodeplate. In such event, current then flows in the resistor 35 connectedbetween the diode plate and ground, which creates a potential dropthereacross. The potential drop developed along the resistor may beutilized to apply bias more negative than normal to an amplifier tube31, or to a plurality of tubes (not shown) which bias becomes more andmore negative as the signal carrier amplitude increases, and vice versa.

The primary function of the automatic volume control network is tocorrelate the gain in the system to the amplitude of an incoming signal,which varies because of fading and because of the distance Vand strengthof the transmitting station. If it is assumed, however, that the signalis relatively constant in amplitude, the diminution of current in theresistor 22, as well as the increase in current in the resistor 35, areindicative of the accuracy of tuning of the receiver, exact tuning beingaccompanied, as is obvious, by respective minima and maxima.

From a consideration of the foregoing, it will be noted that, in myimproved volume control system, there are two potential sourcesavailable which vary in response to the amplitude of an incoming signalimpressed upon the detector tube, namely, the resistor 22 connectedbetween the cathode of the second detector tube and the negativeterminal of the high potential source, and the resistor 35 connectedbetween the diode plate and ground. Either of these sources may beutilized to energize a tuning indicator according to my invention, but Ind it preferable to make use of the cathode resistor rather than thediode circuit resistor for that purpose. Specifically, I nd it expedientto utilize the change in potential across the said resistor to controlthe impedance of a thermionic tube which, in turn, serves as a load upona circuit supplying energy, differentially, to a plurality of lightsources.

Referring to the drawing, I provide a secondary winding 39 on the mainpower transformer 4I which supplies energizing potentials to thereceiver, and connect the primary winding of a step-up transformer 43and a plurality of light sources 45 and 41 in series therewith. Theprimary winding is also tapped at an intermediate point 49, and anadditional light source 5I, or light sources, are connected across thetapped portion.

In the specific system chosen for purposes of illustration, thepotential developed by the Winding on the power transformer whichsupplied the light source is 7.5 volts and each of the lamps is rated at2.5 volts.

The secondary winding of the transformer 43 is connected between theanode 53 and cathode 55 of a therminoic tube 51 of the screen gridpentode type,hereinafter called the control tube, having, in addition tothe said anode and cathode, a suppressor grid 6 I, a control grid 63,and a screen grid 65. A connection 61 including a current limitingresistor 69 extends from the control grid to the cathode of the seconddetector I and a con-- nection 1I extends from the cathode of thecontrol tube to groimd. The screen grid may be connected by a conductor13 to an appropriate point on the bleeder resistor 21, in order thatthey said grid may be maintained at the proper positive potential.

A control tube of the screen grid type is preferable if the changes inpotential available from the resistor 22 are of small magnitude. It isnot to be inferred, however, that my invention is limited to such tubes,since tubes of many other types may be substituted therefor, and, in thespecific circuit illustrated, a three-element control tube may be used,if desired.

When no signal is being received, the cathode of the second detector ispositive with respect to ground, which results in a slight grid currentto the grid of the control tube through the current limiting resistor69. The resistance of the said resistor is large as compared to theresistance of the resistor 22 in the cathode circuit of the seconddetector, and also' with respect to the resistance of the grid of thecontrol tube when it is positive. Accordingly, the grid voltage on thecontrol tube is essentially zero when no signal is being received andthe plate resistance of the tube is minimum, which resistance is reectedto the primary of the transformer.

The low resistance reflected to the primary permits the series-connectedlamps, and`41, to be supplied with energy, and to be lighted toapproximately their full brilliancy, whereas the voltage across thetapped portion of the primary is suiiiciently low that the tube 5i issubstantially deenergized. As a signal is tuned in, thecathode of thesecond detector tube becomes less and less positive, until it reachesground potential with practically no chang-e in illumination of theseries connected lamps because of the practically constant zero biasingpotential still being applied on the control tube.

Further increase in signal amplitude causes the cathode of the seconddetector to assume a potential negative with respect to ground whichresults in a negative bias being applied to the control tube, thuscausing its impedance to increase,

resulting in high impedance on the secondary of the transformer includedin the plate circuit thereof. This increase in impedance in thesecondary of the transformer is reflected into the primary windingthereof and causes a diminution in the potential applied to the seriesconnected lamps, while the potential applied to the shuntconnected lampincreases.

As soon as the station is tuned in to a peak resonant condition, theseries-connected lamps will have minimum brilliancy while the shunt--connected lamp will be giving off its maximum light for the particularsignal strength and sensitivity setting of the receiver.

As pointed out above, the light sources 45 and 41 remain substantiallyfully brilliant until the cathode of the detector tube, by reason ofdecreased current in the resistor 22, becomes slightly negative withrespect to the diode electrode l.

Furthermore, th-e diminution of the brilliancy of the light sources 45and 4l, the application of sufficient potential to the light source 5lto cause it to begin to glow, and the initiation of automatic volumecontrol by the supplying of additional negative potential to thecontrolled amplifier tubes'in the system can only happen when a signalof proper predetermined amplitude is impressed upon the detector tube.If it is assumed that the tubes in the system preceding the detectortube are normally biased, in the absence of signal, to the point atwhich the gain therein is maximum, the action of the light sources isindicative of the correctness of tuning.

On the other hand, if manually controllable means, (not shown), or theequivalent, are provided for making more negativev the normal bias onthe amplier tubes, independent of the automatic volume control network,whereby background noise between stations is minimized during tuning,the receiver may be made so insensitive as to fail to supply sufficientsignal to the detector tube to operate the automatic volume control andto control the light sources.

Under such conditions, the signal from the loudspeaker may be of anyvalue from zero to its value at the threshhold of the automatic volumecontrol system or to the point at which the automatic volume control isdelayed. Such being the case, the fading of the signal cannot becompensated, nor will the volume from the loudspeaker be constant.However, it will be noted, as eX- plained, that the tuning lights willnot respond, which fact indicates to the operator that the adjustment ofthe noise suppressor is such that a constant volume of audio signalcannot be received. If the noise control is then adjusted so that theautomatic volume control can function, the tuning lights respond, whichindicates that the noise suppressor adjustment is such that the signalis substantially unaffected.

It may also be expedient to utilize the rectifier space current in thecontrol tube for either control or indicating purposes through theinclusion of one or more impedance devices in series with the secondaryWinding of the transformer 43. Such devices have been indicated in thedrawing by a plurality of rectangles designated Z.

In connection with the foregoing description of my improved circuit, itshould be noted that a resistor of proper magnitude may be substitutedfor one of the series-connected lamps, or the lamp may be omittedentirely. However, two lamps in series result in somewhat betteroperation of the light system because of the large variation inresistance of the two lamps from low brilliancy to high brilliancy.

It will be noted that the shunt-connected lamp may be of a highervoltage type and may be connected directly across the primary winding ofthe transformer, instead of across only a portion thereof. In thespecific case under discussion, if the lamp is connected across theentire primary, its rated voltage should be approximately 6 volts.

It is also possible to secure the see-saw effect `iust described, asshown in Fig. 2, through the use of a saturating reactor l5, the directcurrent winding of which is included in the plate circuit of one of theradio or intermediate frequency amplifier tubes, or in any other circuitin which the direct current is a function of the amplitude of thereceiver signal. In such event, a light source 'l'l maybe connected inseries with the secondary winding of the power transformer, Whileanother source 19, requiring higher voltage, may be connected in shuntthereto. The principle of operation of the modified circuit isessentially the same as explained in connection with Fig. l of thedrawing, the lamp 'i9 being equivalent to the lamp 5I, while the lamp 11functions in a manner analogous to the operation of the lamps 45 and 41.However, the saturating reactor 15 will not permit as sharp anindication of the tuning as the system previously described and ingeneral the system is not as iiexible in its application.

Should it be desired to utilize indicating lamps requiring the samevoltage, the winding of the saturating reactor 15 may be tapped and alight source 80 be connected thereacross, as indicated by dotted linesin the drawing.

The positions of the tuning indicator lamps are, of course, optionalwith the manufacturer of a radio receiver. I have found it desirable,however, to so dispose both of the lamps that they serve alternately toilluminate a tuning dial, one of the lamps, through any desiredarrangement of color screens, or the like, being utilized to indicatethat the set is exactly tuned in, while the other lamp provides light toassist in the tuning operation.

Specifically,referring to Figs. 3 and 4 of the drawing, I prefer todispose the light 5| behind a translucent dial 8| carrying frequencyindicia, or the like, and surround it with a shield 83 which limits thearea of the dial illuminated thereby. I prefer, also, to so mount theother light sources 45 and 41 below the shield that they illuminate thedial during the tuning operation. Naturally, the several light sourcesmay be arranged in any other desired manner, they may be colored, or

they may be mounted behind-colored screens in order that attractivelighting effects may be had during the tuning operation, Withoutdeparting from the spirit of my invention.

It will, accordingly, be apparent from a consideration of the foregoingdescription of a receiver comprising my improved tuning indicator thatit offers many advantages not heretofore obtainable. For example, it isquite easy to visually tune in any desired station, even though theloudspeaker is not audible, which is desirable in the event that theincoming signal is being reproduced in a situation distant from thepoint at which the receiver itself is located. The visual tuningindication is also much more exact than the indication of tuning givenby the quality and amplitude of the sounds reproduced, since theautomatic volume control device tends to maintain the volume constant,even though, by reason of inaccurate tuning, the amplitude of the signalimpressed upon the second detector is less than it should be.

Advantages other than those enumerated will be readily apparent to thoseskilled in the art to which my invention pertains, as will also manymodifications thereof. My invention, therefore, is not to be restrictedexcept as is necessitated by the prior art and by the spirit of theappended claims.

I claim as my invention:

l. In a radio receiver, a plurality of light sources, means forsupplying alternating potentials thereto and means controllable by anincoming signal for varying the intensity of illumination from one ofsaid light sources in inverse ratio to that from another of said lightsources.

2. In a radio receiver, a plurality of light sources, means capable ofsupplying alternating potentials to said sources, means including atransformer responsive to the condition of sensitivity of said receiverfor determining which of said sources receives potential from saidenergy supply.

3. In a radio receiver, means for correlating the sensitivity thereof tothe amplitude of an incoming signal, a plurality of light sources, meansfor supplying alternating potentials thereto and means including avariable impedance in series with one of said light sources and in shuntwith another of said light sources, said means being responsive to thecondition of sensitivity of the receiver for determining which of saidsources gives off the greater light.

4. In .a radio receiver, a light source, alternating potential supplymeans for energizing said source when the receiver is in syntony withsignals from a desired transmitter, a second light source, andalternating potential supply means for energizing said second sourcewhen the receiver is not in syntony with signals from the desiredtransmitter, whereby, through observation of the condition ofillumination of said sources, the exactness of tuning of the receivermay be judged.

5. In an amplifier, a light source, an alternating current supplycircuit connected to said source, a step-down transformer, the primarywinding of which is included in said circuit, a. thermionic device, thespace current path in Which is in series With the secondary Winding ofsaid transformer, and signal-responsive means for varying the impedanceof said thermionic device.

6. In a radio receiver, a plurality of light sources, means forsupplying alternating potentials thereto, .a turning indication deviceadapted to be illuminated by said light sources, means for screeningcertain portions of said tuning indication device from illumination byrespectively different ones of said light sources, and means controlledby an incoming signal for varying the intensity of illumination from oneof said light sources in inverse ratio to that from another of saidlight sources.

7. In a radio receiver, a receiving network, a source of automaticvolume control potential therefor, a transformer having a primaryWinding and a secondary winding, a tube having an anode circuitconnected with said secondary winding whereby said tube is a load uponsaid transformer, a tuning indicator, a source of light associatedtherewith, an energizing circuit including at least a portion of saidprimary winding for supplying alternating current to said light source,means for applying the potential from said .automatic volume controlsource to said tube to control the effectiveness of the load upon saidtransformer, and means for adjusting the impedance of said tube wherebysignal variations cause the load upon said transformer to vary betweenlimits adapted to cause an indicating change in the illumination of saidlight source.

8. In a radio receiver, a receiving network, a source of .automaticvolume control potential therefor, a saturatable reactor, a tube havingan anode circuit, said reactor being connected with said anode circuitto receive saturating current therefrom, a tuning indicator, a lampassociated therewith, a lamp energizing circuit including at least aportion of said reactor for supplying a1- ternating current to saidlamp, means for applying said potential from said automatic volumecontrol source to said tube to control the flow of saturation currentwhereby to cause an indicating change in the illumination of said lamp.

9. Radio receiving apparatus comprising, in combination,signal-selecting means tunable to receive any signal of specifiedfrequency in a band of frequencies, signal-amplifying means foramplifying the signals thus received, incandescent indicating meansconnected to said amplifying means for producing variations in light inaccordance with the average current flowing through said amplifyingmeans, .and light-diffusing means for rendering readily perceptiblesmall variations in the light produced by said indicating means,indicative of small variations in the tuning of said selecting means.

LOY E. BARTON.

